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Filling and Sealing the Tube.—By means of a thistle
funnel with a long stem, about 5 c.c. of fuming nitric acid are first
introduced, and the funnel carefully withdrawn so as
not to wet the side of the tube.    About 0*5 gram silver
nitrate in crystals is dropped in, and finally the narrow
weighing-tube containing o'2—03 gram of substance
is slipped to the bottom  of the tube (see Fig. 21).
Bromacetanilide (see Prep. 55, p. 152) may be  used
for this estimation.     The open end of the tube is now
sealed  in  the  blow-pipe.     This   operation   requires
some care and a little skill.    About two inches of the
tube at the open end is very gradually heated by re-
volving it for several minutes in the smoky flame of
the blow-pipe.    The tube is now  grasped about the
middle with the left hand, and inclined at an an<'le of
about 45°.    The blast is turned on slowly, and the end
of the tube heated and revolved until the glass begins to soften.
The end of a glass rod, about 13 cm. (5 in.) long, held in the
right hand, is heated at the same time.    The glass rod is then

FiG. :

FIG. 22.

used to press the edges of the glass tube together, as shown in
Fig. 23. The subsequent operation depends upon whether
soft or hard glass is to be manipulated. If soft glass is used,